Power converter circuits with an AC/DC converter and a DC/DC converter can be configured to receive an AC input voltage and to provide a DC output voltage to a load. Many electronic devices, such as computers, TV sets, etc., or batteries that have to be charged, require a DC voltage as an input voltage, while the supply voltage that is available from the power grid is an AC voltage. In these cases an AC/DC conversion, that converts the AC input voltage into a DC output voltage, is required. In particular in those cases, in which the power consumption of the load is higher than several 10 W, additionally to the power conversion, a power factor correction is required. The power factor correction serves to minimize the reactive power and to maximize the real power taken from the grid.
A power converter circuit that provides power factor correction includes a power factor corrector (PFC) and a DC/DC converter coupled to the PFC. The PFC acts as a AC/DC converter and is usually a boost converter that generates a DC voltage that is higher than the amplitude (peak value) of the AC input voltage from the AC input voltage. The DC/DC converter converts the DC voltage provided by the PFC into a DC output voltage supplied to the load voltage. The input voltage and the input current of the PFC have a sine waveform. When the power factor of the PFC is close to 1, such as between 0.97 and 1, the input voltage and the input current are almost in phase, so that the input power of the PFC has a sine squared (sin2) waveform that cause ripples of the PFC output voltage. In order to reduce the amplitude of those ripples, a capacitor that is also referred to as DC link capacitor, is connected between output terminals of the PFC.
The DC link capacitor may have a capacitance of up to several mF (milli-Farads) and is usually implemented as an electrolytic capacitor. However, electrolytic capacitors have a relatively short lifetime, have high leakage currents, and are expensive.
Power converters with a DC/DC converter and DC/AC converter can be configured to receive a DC input voltage from a voltage source, such as a solar panel, a battery, or the like, and to generate an AC output voltage, that may be supplied to a power grid. In those applications, the DC/DC converter is usually implemented as a boost converter that generates a DC output voltage that is higher than the peak voltage of the desired AC output voltage. The DC/AC converter (inverter) converts the DC output voltage of the DC/DC converter into an AC output voltage. The output voltage and the output current of the DC/AC converter have a sine waveform. When the output voltage and the output current are in phase the output power of the DC/AC converter has a sine squared (sin2) waveform, while the input power it receives from the DC/DC converter is constant at a given input power of the DC/DC converter. In order to reduce ripples of the DC input voltage of the DC/AC converter that may negatively affect the function of the DC/DC converter a capacitor is connected between the input terminals of the DC/AC converter.
This capacitor may have a capacitance of up to several mF (milli-Farads) and is usually implemented as an electrolytic capacitor. However, electrolytic capacitors have a relatively short lifetime, have high leakage currents, and are expensive.
There is, therefore, a need to provide a power converter circuit with a DC/DC converter and a DC/AC converter in which the size of a capacitor connected between input terminals of the DC/AC converter can be reduced without degrading the power conversion efficiency.